The invention relates to a method for applying a projection to a metal layer of a cylinder-head gasket as it is used in an internal combustion engine and to a cylinder-head gasket.
It is known from published German Patent Application 196 11 092 to apply a projection to a metal layer of a metallic cylinder-head gasket for an internal-combustion engine having at least one functional metal sheet, which is provided with one opening or a plurality of adjacent openings depending on the number of combustion chambers of the internal-combustion engine, a bead being provided in the at least one elastic metal sheet around each opening, at a distance from the latter, so that a straight section of sheet metal is left clear in the region of the edge of the opening, for which bead a spring travel limiter or so-called stopper, which runs coaxially with respect to the bead and is formed by the projection, is provided, the projection consisting of a sufficiently temperature-resistant thermosetting plastic with a high mineral filler content. A spring travel limiter or so-called stopper of this type has to fulfil the requirement that it must not be deformed under the compressive and thermal loads at the edge of the combustion chamber, i.e. must be virtually inelastic. However, suitable thermosetting plastics then have the drawback of being brittle, with the result that the spring travel limiter which is formed by the projection may break during handling and installation.
It is an object of the invention to provide a method used during the production of cylinder-head gaskets, which process allows forming plastic stoppers, which are designed as projections, in such a way that they are substantially inelastic under the compressive and thermal loads to which they are exposed in an internal-combustion engine.
It is a further object of the invention to provide a method to form a stopper which does not break during handling and installation.
Still a further object of the present invention is to provide a cylinder-head gasket having one or more stoppers of plastic material which are substantially inelastic under the compressive and thermal loads to which they are exposed in an internal-combustion engine.
In one aspect, the invention is thus a method for applying a projection to a metal layer of a metallic cylinder-head gasket for an internal-combustion engine having at least one elastic metal sheet, which is provided with at least one opening depending on the number of combustion chambers of the internal-combustion engine. A bead is provided in the at least one elastic metal sheet around each opening, at a distance from the latter, so that a straight section of sheet metal is left clear in the region of the edge of the opening, for which bead a stopper, which runs coaxially with respect to the bead and is formed by the projection, is provided. The projection is produced from a mixture which contains a plastic with a high mineral filler content, especially a mixture of an elastomer with a filler which has been surface-treated by means of a silane.
A further aspect of the invention is a metallic cylinder-head gasket for an internal-combustion engine having at least one elastic metal sheet which is provided with at least one opening depending on the number of combustion chambers in the internal-combustion engine, a bead being provided in the at least one elastic metal sheet, around each opening at a distance from the latter, so that a straight section of metal sheet is left clear in the region of the edge of the opening, for which bead a stopper, which runs coaxially with respect to the bead, is provided. The at least one projection consists of a plastic with a high mineral filler content, especially an with a filler which has been surface-treated with a silane.
The use of fillers which have been surface-treated with a silane, for example, an aminosilane or an epoxysilane, to produce an elastomer with a high filler content, from which stopper-like projections are formed on one or more metal layers of a single-layer or multilayer metallic cylinder-head gasket, for example, by screen printing or the automatic application of a bead, surprisingly results in projections or stoppers which satisfy both contradictory requirements. Moreover, the result is a very simple, inexpensive process for forming the projections which readily makes it possible to employ both layers of a uniform thickness and width and layers which vary in thickness and width, by suitably designing a screen which is used for the screen printing.
The compressive strength of the elastomer is provided by suitable filling with the surface-treated filler. In this case, a plastic/filler ratio of 1:1 to 1:5, in particular 1:2.5 to 1:4, is expedient. The filler used is preferably a filler which has a low coefficient of thermal expansion, for example, silica flour (particularly preferred), aluminium oxide, rutile, dolomite or wollastonite.
Particularly, suitable elastomers are fluororubber or fluorosilicone rubber. Typical solvent-containing formulations may be made up as follows:
Surprisingly, it has been found that cylinder-head gaskets with projections with a composition of this nature withstand the loads which are imposed when used in engines.
Further embodiments of the invention may be taken from the following description and the claims.